1. Field of the Invention
The present invention relates to a zoom lens system suitable for a single-lens reflex camera.
2. Related Background Art
In a focusing method of a zoom lens system, there has been a widely used method that the most object side lens group, which is a first lens group, is drawn out. In this method, there is an advantage that the moving amount for focusing does not depend on the zooming position and is determined by a distance to the object, so that it is effective for simplifying the focusing mechanism. However, a plurality of lenses have to be moved for focusing, and the weight of the focusing lens group tends to become heavy, so that it becomes difficult to make focusing speed for autofocus faster. In order to solve the problem, a method has been proposed that the first lens group divided into a front lens group having positive refractive power and a rear lens group consisting of a single lens having positive refractive power, and focusing is carried out by moving only the rear lens group to the object side so as to reduce weight of the focusing lens group (see, for example, Japanese Patent Application Laid-Open No. 6-51202).
However, in each embodiment disclosed in Japanese Patent Application Laid-Open No. 6-51202, the moving amount of the focusing lens necessary for focusing is still large, so that focusing speed in autofocus is not sufficient.